The present invention is directed to a method for producing a semiconductor laser device having a pair of closely spaced semiconductor lasers in order to achieve interlaser spacings of approximately 2 .mu.m. Such a device may be incorporated in numerous devices including optical disk readers or flying spot scanners (commonly referred to as raster output scanners (ROSs)). A flying spot scanner typically has a reflective multifaceted polygon mirror that is rotated about its central axis to repeatedly sweep one or more intensity modulated beams of light across a photosensitive recording medium in a linear or fast-scanning direction. Printers employing multiple intensity-modulated beams are referred to as multibeam or multispot printers. In such printers the dual lasers are considered to be an enabling technology for high speed operation at resolutions of about 600 spots per inch (spi). The present invention utilizes integrated alignment devices which are formed on the surfaces of the semiconductor wafers from which the laser diode dies are produced to accurately position a pair of laser dies with respect to one another. Furthermore, a small air space generally separating the two laser dies provides thermal, electrical and optical isolation therebetween.
The desirability of a multiple beam semiconductor laser has been recognized previously. However, because of thermal crosstalk between closely spaced laser diodes, practical interlaser spacings have generally been limited to spacings of at least 100 .mu.m. Designs intended to achieve close spacing of the emitted laser beams are known, of which the following disclosures which may be relevant:
U.S. Pat. No. 4,901,325 PA0 Patentee: Kato et al. PA0 Issued: Feb. 13, 1990 PA0 U.S. Pat. No. 4,870,652 PA0 Patentee: Thornton PA0 Issued: Sep. 26, 1989 PA0 U.S. Pat. No. 4,796,964 PA0 Patentee: Connell et al. PA0 Issued: Jan. 10, 1989 PA0 U.S. Pat. No. 4,403,243 PA0 Patentee: Hakamada PA0 Issued: Sep. 6, 1983
The relevant portions of the foregoing patents, hereby incorporated by reference for their teaching, may be briefly summarized as follows:
U.S. Pat. No. 4,901,325 teaches a semiconductor laser device used in an optical disk device which utilizes a pair of semiconductor laser chips and a fixing device for fixing the laser chips so that the electrode surfaces are approximately parallel and opposite to each other. The fixing device comprises either a single-piece, U-shaped block or, alternatively, a pair of blocks, upon which the photodiodes are ultimately mounted. When a pair of blocks are used, a tooling system (see FIG. 9) is used to align and permanently affix the blocks to a base plate under the control of a vision system which enlarges and processes an image region centered on the active regions of the lasers affixed thereto.
U.S. Pat. No. 4,870,652, discloses a monolithic high density array of independently addressable semiconductor lasers. The lasers are further characterized as having emitters on closely spaced, 3-10 .mu.m, centers, without displaying phase locking and with minimal crosstalk effects. The monolithic, independently addressable array is suitable for use with high speed laser printers, laser disk technology, and fiber optic communication.
U.S. Pat. No. 4,796,964 describes a method for using a multiple emitter solid state semiconductor laser in a raster output scanner. The overlapping beams are sequenced in ON/OFF operation to avoid any inter-beam interference in a manner that assures that only one laser beam will be on at any given time. Hence, nonuniformity caused by optical interference of overlapping beams is prevented without the need for further modification of the optical properties of the beams (e.g., polarization and wavelength).
U.S. Pat. No. 4,403,243 teaches a laser apparatus including support and soldering means for a light transmitting member which is affixed so as to allow transmission of an emitted laser beam generated within the apparatus by a semiconductor laser. The light transmitting, by soldering, becomes hermetically sealed to a support member, thereby completely encapsulating the laser source.